I was just thinking about Estelle last night. I'm pretty sure she will be a bridesmaid, but I can't foresee the (very) near future of course. She would be an adorable bridesmaid. I can just imagine her in a little bridesmaids dress with a poesy of flowers. I wonder who else will be in the bridal party. I don't know anything about the Hellqvists, but perhaps Sofia has some younger cousins or friends with young children who could be bridesmaids and page boys.
I can imagine that the wedding will be 'big', considering that the engagement celebrations were grand for a Prince who is third in line to the throne. It will be interesting to see if it will remain a family and friends affair, or if some foreign royals will be invited too. IIRC there weren't any foreign royals at Madeleine and Chris's wedding. Victoria and Daniel's wedding was an exception, since she is the heiress.